From fcdc130d71ba85a741f91aacc1787e241502438e Mon Sep 17 00:00:00 2001
From: atharva-satpute <55058959+atharva-satpute@users.noreply.github.com>
Date: Wed, 16 Aug 2023 12:25:23 +0530
Subject: [PATCH] Reject bad values in `SparsePauliOp.paulis` setter (#10437)

* Fix Sparse pauli setter to update dimension info

* Fix Sparse pauli setter to verify dimension info

Value error will be raised if:
1. Number of qubits are not equal
2. Number of elements in PauliList are not equal

* Add tests

* Add release note

---------

Co-authored-by: Jake Lishman <jake.lishman@ibm.com>
Co-authored-by: Ikko Hamamura <ikkoham@users.noreply.github.com>
(cherry picked from commit fe87015a901b8b84dba03b201409a2dc545825f2)
---
 .../quantum_info/operators/symplectic/sparse_pauli_op.py  | 8 ++++++++
 ...pauli-op-constraint-pauli-setter-52f6f89627d1937c.yaml | 6 ++++++
 .../operators/symplectic/test_sparse_pauli_op.py          | 8 ++++++++
 3 files changed, 22 insertions(+)
 create mode 100644 releasenotes/notes/sparse-pauli-op-constraint-pauli-setter-52f6f89627d1937c.yaml

diff --git a/qiskit/quantum_info/operators/symplectic/sparse_pauli_op.py b/qiskit/quantum_info/operators/symplectic/sparse_pauli_op.py
index 95162ebe247d..cee5300049e4 100644
--- a/qiskit/quantum_info/operators/symplectic/sparse_pauli_op.py
+++ b/qiskit/quantum_info/operators/symplectic/sparse_pauli_op.py
@@ -235,6 +235,14 @@ def paulis(self):
     def paulis(self, value):
         if not isinstance(value, PauliList):
             value = PauliList(value)
+        if value.num_qubits != self.num_qubits:
+            raise ValueError(
+                f"incorrect number of qubits: expected {self.num_qubits}, got {value.num_qubits}"
+            )
+        if len(value) != len(self.paulis):
+            raise ValueError(
+                f"incorrect number of operators: expected {len(self.paulis)}, got {len(value)}"
+            )
         self._pauli_list = value
 
     @property
diff --git a/releasenotes/notes/sparse-pauli-op-constraint-pauli-setter-52f6f89627d1937c.yaml b/releasenotes/notes/sparse-pauli-op-constraint-pauli-setter-52f6f89627d1937c.yaml
new file mode 100644
index 000000000000..86d4b552ffe4
--- /dev/null
+++ b/releasenotes/notes/sparse-pauli-op-constraint-pauli-setter-52f6f89627d1937c.yaml
@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    The setter for :attr:`.SparsePauliOp.paulis` will now correctly reject attempts to set the
+    attribute with incorrectly shaped data, rather than silently allowing an invalid object to be
+    created.  See `#10384 <https://github.com/Qiskit/qiskit-terra/issues/10384>`__.
diff --git a/test/python/quantum_info/operators/symplectic/test_sparse_pauli_op.py b/test/python/quantum_info/operators/symplectic/test_sparse_pauli_op.py
index be066453a78d..767153e23883 100644
--- a/test/python/quantum_info/operators/symplectic/test_sparse_pauli_op.py
+++ b/test/python/quantum_info/operators/symplectic/test_sparse_pauli_op.py
@@ -1015,6 +1015,14 @@ def test_assign_parameters(self):
         with self.subTest(msg="fully bound"):
             self.assertTrue(np.allclose(bound.coeffs.astype(complex), [1, 3, 6]))
 
+    def test_paulis_setter_rejects_bad_inputs(self):
+        """Test that the setter for `paulis` rejects different-sized inputs."""
+        op = SparsePauliOp(["XY", "ZX"], coeffs=[1, 1j])
+        with self.assertRaisesRegex(ValueError, "incorrect number of qubits"):
+            op.paulis = PauliList([Pauli("X"), Pauli("Y")])
+        with self.assertRaisesRegex(ValueError, "incorrect number of operators"):
+            op.paulis = PauliList([Pauli("XY"), Pauli("ZX"), Pauli("YZ")])
+
 
 if __name__ == "__main__":
     unittest.main()